1 Fusion-Bonded Epoxy (FBE) and Dual-Layer FBE Materials Provide Enhanced Performance for Pipeline InstallationBy: J. Alan Kehr, Martin Rau, and Emran Siddiqui; 3M Company SUMMARY Fusion Bonded Epoxy (FBE) and 3 Layer P olyolefin (3LPO) are the most commonly used pipeline coatings in the world. Over the last few years, dual Layer FBE (DLFBE) coating s have seen more use because of combining properties of a coating that is non-shielding to cathodic protection and the low-cost economics of FBE with damage resistance approaching that of 3 Layer Polypropylene (3LPP) and 3 Layer Polyethylene (3LPE). FBE BASED COATING SYSTEMS FBE Single Layer. Since first introduced in 1960, single-layer FBE has proven its capability as a pipeline coating and is now the most commonly used pipeline coating in North America. It not only has the performance characteristics important to the application and construction processes, but also has proven perfor mance in undergroun d and undersea service over a lo ng period of time. It has proven effective for line pipe, girthwelds, fittings, and bends. When used at a greater thickness, it has worked effectively with weight concrete and directional- bore installations. FBE Two Layer. Utilizing two layers of FBE provides great versatility in coatings forpipeline protection. Two-layer FBE systems utilize the application of a second FBE on top ofthe base FBE corrosion coating. The top layer typically, but not necessarily, is deposited during the melt (pre-gelation) stage of the primary layer. The result is an intimate chemical bond between the two layers. A si gnificant advantage of multilayer techn ology is that unique characteristics can be developed by selection of different coating layers with specific properties. Each layer can be designed to impart specific characteristics that combine to produce performanc e results that significantly exceed those of a single-layer co ating. The first layer has the properties of a standalone FBE coating, providing excellent adhesion and resistance to cathodic disbondment. The top layer provides mechanical damage resistance from impact or gouging during handling, transportation, and construction. The combination provides the contractor faster, wor ry-free installation and the pipeline owner with improved underground coating performance. This system has been used successfully with impingement and compression-wrapped weight concrete ap plications. The pipeline construction services industry has created girthweld coating application systems that can apply dual-layer FBE in the field so that the entire pipeline has the same coating.
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Fusion-Bonded Epoxy (FBE) and Dual-Layer FBE Materials
Provide Enhanced Performance for Pipeline Installation
By: J. Alan Kehr, Martin Rau, and Emran Siddiqui; 3M Company
SUMMARY
Fusion Bonded Epoxy (FBE) and 3 Layer Polyolefin (3LPO) are the most commonly used
pipeline coatings in the world. Over the last few years, dual Layer FBE (DLFBE) coatings
have seen more use because of combining properties of a coating that is non-shielding to
cathodic protection and the low-cost economics of FBE with damage resistance approaching
that of 3 Layer Polypropylene (3LPP) and 3 Layer Polyethylene (3LPE).
FBE BASED COATING SYSTEMS
FBE Single Layer. Since first introduced in 1960, single-layer FBE has proven its capability
as a pipeline coating and is now the most commonly used pipeline coating in North America.
It not only has the performance characteristics important to the application and construction
processes, but also has proven performance in underground and undersea service over a long
period of time. It has proven effective for line pipe, girthwelds, fittings, and bends. When
used at a greater thickness, it has worked effectively with weight concrete and directional-
bore installations.
FBE Two Layer. Utilizing two layers of FBE provides great versatility in coatings for
pipeline protection. Two-layer FBE systems utilize the application of a second FBE on top of
the base FBE corrosion coating. The top layer typically, but not necessarily, is deposited
during the melt (pre-gelation) stage of the primary layer. The result is an intimate chemical
bond between the two layers. A significant advantage of multilayer technology is that unique
characteristics can be developed by selection of different coating layers with specific
properties. Each layer can be designed to impart specific characteristics that combine to
produce performance results that significantly exceed those of a single-layer coating.
The first layer has the properties of a standalone FBE coating, providing excellent adhesion
and resistance to cathodic disbondment. The top layer provides mechanical damage resistance
from impact or gouging during handling, transportation, and construction. The combination provides the contractor faster, worry-free installation and the pipeline owner with improved
underground coating performance. This system has been used successfully with impingement
and compression-wrapped weight concrete applications. The pipeline construction services
industry has created girthweld coating application systems that can apply dual-layer FBE in
the field so that the entire pipeline has the same coating.
coating system is based onearlier pipeline coatings
and combines FBE and
polyolefin materials to
offer customized systems
designed to fulfil
environment requirements.
This system is an effective
solution in situations where
extraordinary coating
damage is highly probable
or elevated temperature
service is likely.
The three types of FBE based coating systems have a relatively long history as seen in Figure
1.
MECHANISM OF CORROSION
One general definition of corrosion is the degradation of a material through environmental
interaction.
As extracted from its ores (metal oxides: Hematite Fe2O3, Bauxite Al2O3·H2O), a significant
amount of energy is put into metal placing it in a high energy state. In accordance to one of
the principles of thermodynamics, materials will always seek the lowest energy state. In caseof metals they tend to lose their energy by reverting to compounds more or less similar to
their original states, which in most cases is an oxide or some other compound. This process by
which metals convert to the lower energy oxides is called corrosion. Corrosion occurs for
most common engineering materials at ambient temperatures in water-containing
environments. The aqueous environment and its electrochemical nature are also referred to as
the electrolyte and, in case of underground pipelines, is the moist soil.
The corrosion reaction chemistry is electrochemical in nature. When metal atoms are exposed
to an environment containing water molecules, they can give up electrons (oxidation)
becoming themselves positively charged ions provided that an electrical circuit can be
completed. The oxidation is called the anodic reaction. The consumption of those electrons by
the reduction reaction of oxygen or water is commonly called the cathodic reaction. Theoxidation reaction causes the actual metal loss, but the reduction reaction must be present to
consume the electrons liberated by the oxidation, maintaining charge neutrality. Otherwise, a
large negative charge would rapidly develop between metal and electrolyte and the corrosion
process would cease.
CORROSION PREVENTION
The principal methods for corrosion prevention on underground pipelines are coatings and
cathodic protection.
Figure 1. A truncated history of pipeline coatings.
Coatings are intended to form a continuous film of an electrical insulating material over the
metallic surface to be protected. The function of such a coating is to isolate the metal from
direct contact with the electrolyte, interposing a high electrical resistance so that
electrochemical reactions cannot occur.
FBE systems are effective in the prevention of underfilm corrosion due to their excellent barrier properties including low oxygen permeability. Oxygen permeability of FBE is less
than one-fifth that of polyethylene. However, FBE coatings have a higher moisture
permeability rate than PE coatings.
Cathodic Protection (CP) is a technique to reduce the corrosion rate of a metal surface by
making it the cathode of an electrochemical cell. This is realized by shifting the potential of
the metal in the negative direction by use of an external power source. For CP to work,
current must be discharged from an earth connection called a ground bed. In the process of
discharging the current in a sacrificial system, the anodes in the ground bed are consumed by
corrosion.
COATINGS
Single Layer FBE. Since a New Mexico company coated the first FBE pipeline in 1960, this
technology is now the number one pipeline-coating in North America. It is used on pipes,
bends, girthwelds, and fittings. It is also used in the oil, gas, and water markets. It has been
installed in the ocean, the arctic, in the mountains and in the plains. 1 Figure 2 shows the
improvement in cathodic disbondment resistance of FBE pipecoatings in the last fifty years.
FBE Cathodic-Disbondment-
Resistance Improves with Chemistry
90 days, 23
o
C, 3% ASTM G 8 electroly te, -1.5 V
0
5
10
15
20
25
30
35
1965 1980 1995
Year
C a t h o d i c D i s b o n d m e n t - m m r
Figure 2. There have been significant improvements in FBE coating technology in the
Long years of experience demonstrate the following benefits for single layer FBE:
1. Excellent adhesion to steel; good chemical resistance
2. Non-shielding to CP – if it fails, it fails friendly
3. No reported cases of stress-corrosion cracking (SCC) of pipe coated with FBE
4. Resistant to biological, insect, termite, and root attack
5. Installation friendly• Excellent penetration resistance, good abrasion and gouge resistance
• Good impact resistance
o Impact damage is limited to the point of contact
o Damage is easily seen
o Damage is easily repaired
• Good flexibility
Dual Layer FBE. The first dual-layer FBE (DLFBE), introduced in 1992, was for high-
operating temperature pipelines. That was followed in 1998 by the first abrasion resistant
outer (ARO) coating for directional drill pipeline installation. DLFBE, see Figure 3 maintains
the excellent performance and installation characteristics of single-layer FBE, but provides
even better damage resistance, with a slight reduction in flexibility. The dual-layer system provides many of the advantages of three-layer systems – see Table 1.
The ARO system utilizes a high performance FBE as a base layer with a top coat of a
mechanically hard FBE, which ensures a tough outer layer resistant to gouge, impact,
abrasion and penetration. Today’s dual FBE system is sometimes used for the entire pipe line
length (Kern River project, 1150 km of 30 and 42 inch pipe at a nominal thickness of 500
microns; Koyali-Ratlam pipeline Project in India, 262 km).
Figure 3. Dual Layer FBE systemThe relative cost between single-layer FBE, dual layer FBE, and three-layer polyolefin
coating systems depend on many variables, such as: commodity (solid epoxy, PE) costs that
affect coating materials, applicator plant productivity, and coating thickness specifications.
Those costs will also vary from region to region and applicator to applicator. Pipe diameter
and wall thickness can play a role because most specifications call for increased polyolefin
thickness as pipe diameter goes up – see Figure 4.
X-cut adhesion test. A knife or sharp razor blade is used to cut an “X” in the coating to the
substrate at an approximate 30° angle – see Figure 7. A knifepoint is used to flick the coating
at the point of intersection. Normally, the coating cuts and breaks cohesively, but does not
peel as a result of the flicking action, leaving coating attached to the substrate.
Moderate adhesion results in small chips removed from the steel surface. Poor adhesionresults in removal of large intact pieces of the coating. Test results have to be carefully
evaluated as they can give erroneous results if the coating has softened or has porosity.
Chemical Resistance
Epoxies are well recognized for having good chemical resistance. There are differences
depending on the formulation, e.g., acid-anhydride-cured coatings generally have better acid
resistance than amine-cured systems and less resistance to bases.5
However, amine-cured FBE
still has excellent resistance to both acids and bases. A rule of thumb for FBE pipelinecoatings is that if the pH is measurable with paper, i.e., pH of 2 to 13, the coating will perform
well in the environment. Generally, hydrocarbon spills do not attack FBE pipeline coatings.6, 7
Soil chemicals do not typically attack an FBE coating. Some chemicals may affect the
cathodic-disbondment reaction and accelerate or slow the loss of adhesion around a holiday,
but do not attack the coating itself. If there is a holiday and insufficient or no cathodic
protection, a corrosive agent such as acid will attack the exposed metal and corrosion can
undermine the coating.
If there are no holidays, a coating performs better in salt water than in fresh water. Fresh or
deionized water has a higher osmotic gradient and, if contaminants are present under the
coating, causes blistering faster than salt water.
FBE coatings are resistant to damage by solvents. Some, such as alcohols, can soften an FBE
and cause it to swell, increasing susceptibility to damage. Oxidizing agents can also attack the
coating, resulting in thickness loss. Pipelines through landfills, chemical dumps, or around
chemical plants may be susceptible to chemical attack. Higher temperatures normally
accelerate any chemical reaction. Checking with the coating manufacturer provides guidance
for concerns about exposure to solvents, oxidizing agents, or chemical dumps.8
A World War II study demonstrated that to avoid fungal or bacteria attack, the coating should
be formulated with materials that cannot be used by biological organisms for food.9
A 1969 study of over twenty epoxy coatings, including two early FBE pipe coatings, showed
them to be funginert according to Method 508 of Specification MIL-STD-810B.10, 11
Termite resistance of FBE coatings was demonstrated in a 1975 Australian study. After
exposure, following the procedure of Gay, Greaves, Holdaway, and Wetherly, to 84 days in
colonies of Coptotermes acinaciformis and Mastotermes darwiniensis, the two FBE pipe
coatings were undamaged.12
The visual assessments followed those by Gay and Wetherly.13, 14
Even under a microscope no surface nibbles were seen on the FBE.
In contrast, samples of vinyl and PE tape, heat-shrink sleeves, extruded PE, and coal tar all
suffered damage from Coptotermes acinaciformis. All but the shrink sleeve and one of the
extruded PE coatings were attacked by Mastotermes darwiniensis.
Non-Shielding
An electrical shield can be defined as a barrier of any nature that will prevent or divert from a
pipeline the flow of CP current. This electrical shielding may result from a non-metallic
insulating barrier or from the diversion of the current to another metallic structure in the
electrical path between the ground bed and the pipeline to be protected.
Current Requirements vs. Coating Type
Log Scale - Canadian Experience
1
10
100
1000
FBE PE CTE AE
Coating Type
C u r r e n t - m i c r o A / m 2
0
15
Years
Figure 8. Current requirement measurements by a major Canadian gas companyshowed a significant difference among pipecoatings in their system. FBE = Fusion
Bonded Epoxy single layer, PE = two-layer PE utilizing a rubberized asphalt adhesive,
CTE = coal-tar enamel, and AE = asphalt enamel.
If the barrier is an insulating material sufficiently porous to absorb moisture and become
conductive, enough current may pass to ensure a CP of the pipe. Such a barrier will not then
removing residual contaminants. If properly done, this can be considered as an insurance
policy that protects against unknown, unexpected or not observed contamination.
Good performance of all coatings is a function of proper pipe surface conditioning and
preparation. No matter what coating system is in use, if the surface has proper profile and
peak, the cleaner the pipe surface, the better the coating performance is.
Flexibility
Most pipelines require bending to meet the contours of the landscape or the installation
process16, 17
– see Figure 10. For sharp bends, the pipe is bent first and then coated.
Figure 10. Laboratory tests (A) are able to demonstrate bendability comparable to field
experience and are useful for comparing coatings. Photo (B) shows a field bend in
process. Photo (C) illustrates the use of a reel barge for offshore pipe installation. Reel-
barge installation requires greater coating flexibility because of smaller radius bends.
Flexibility requirements are greatest for pipe at the reel core and diminish withsucceeding layers of pipe. The coating must be designed to meet the core bending
requirements. Photograph (D) shows pipe bent to fit the contours of the land.
Impact Resistance
Any organic material caught between a rock and a hard place, e.g., steel, is going to suffer.
The range of impact force during pipe handling and installation varies greatly depending on
handling techniques, accidents, and procedures.
Improved impact resistance means less damage. FBE coatings have several valuable
characteristics when it comes to impact damage:
• Good impact resistance• Impact damage is limited to the contact point
• Damage is easily seen
• Damage is easily repaired
For some coating systems, damage extends beyond the impact zone. For FBE coatings, the
damage is normally limited to the point of collision. Unlike some coatings that disbond
without complete penetration, the damage for FBE coatings is easily seen. Two-part liquid
coatings or hot-melt patchsticks make the repair easy. When total damage and cost of repair
are taken into account, FBE may provide the best economic answer.
substrate is thin enough to deform, it absorbs much of the force and allows the coating to
survive intact.
There are several ways to improve impact resistance utilizing dual-layer FBE systems. In
designing dual coat systems for high impact resistance, both the design of the basecoat and
the topcoat are important.
Dual-coat technology can provide significant performance improvement without a major economic penalty. See Figure 12, a dual coating system at the same thickness of a stand-alone
Abrasion resistance is a factor in many performance situations – see Figure 13 for a backfill
example. During transportation, cinders and grit can get between pieces of pipe. For that
reason, there should be separators to prevent intimate contact between pipe joints. Normal
handling often includes accidental dragging along a hard surface, such as wood supports.
Abrasion also takes place during directional drill installation and back filling.
In summary, FBE and DLFBE coating systems provide a balance of properties suitable for most pipeline installations.
FBE/DLFBE COATINGS AND CATHODIC PROTECTION IN THE FIELD
Earlier discussions in this paper have been theoretical and based on laboratory tests. This
section will provide actual examples of observations and measurements on pipelines and is in
the form of case histories.
Case History 1 – Large Diameter Pipeline in Western US
The project includes two parallel pipelines 36" in diameter by about 1100 km in length. 18The
first pipeline was coated and installed in the early 90s with single layer FBE. The second line
was installed in about 2003 and coated with dual layer FBE with a nominal thickness of 22
mils (550 microns) of dual layer FBE. The current requirements of the original pipeline wereso low that they did not add additional CP equipment beyond connecting the two pipelines.
They did upgrade the CP systems for the compressor stations.
Figure 13. While FBE coatings resist damage from impact
and abrasion, specialized equipment is available to remove
large rocks from the ditch-excavation spoils and apply thesized materials directly into the ditch. Photo courtesy of
The pipelines are interlinked with six compressor stations. Even though they have their own
CP systems, some of the current from the pipelines also feeds the compressor stations and
current readings are higher because of that. There is bare copper at each station and the last
ground bed also must protect zinc ribbon used to dissipate current from an overhead line. The
actual current required to protect the FBE coated lines is less. The total current required to
protect the 2189 km of 36” pipe was 136 amps for an average of 21.7 microamps per square
meter. Average distance between groundbeds to protect the dual lines was 57.56 km. Pleasesee Figure 14 for current required for each groundbed as measured on April 11, 2008. at that
time, one of the lines was 16 years in the ground and the other five years. Also see Table 2 for
a summary of the pertinent pipeline statistics.
Figure 14. Current requirements on each groundbed as measured on April 11, 2008 on
1100 km parallel pipeline, one coated with FBE and the other with DLFBE.
Table 2 Details on the Case History 1 pipeline.
Total Pipeline length 2189 km
Micro amps/m2 21.7
Average d is tance between groundbeds 57.6 km
Case History 2 – Two FBE Coated Projects in Eastern US
Project 1 = 11 miles of 24" OD pipe in the Northeastern US
Project 2 = 9.5 miles of 20" OD pipe in the Northeastern US
Project supervision reported that the coated pipe handles and transports with little damage as
long as contractors handle adequately.19
No feedback from contractors on either project. No
information was gathered on current density except at directional drilled sites. This was FBEwith an abrasion resistant overlay. Current density on the horizontal directional drill (HDD)
lines was measured from around 0.5 to 16 microamps/meter squared/100 mV.
The key finding in this case history was that even after directional drill installation, the
current requirements ranged from only 0.5 to 16 µA/m2.
Case History 3 – FBE Coated Line in US
This project was a 133 km single layer FBE line. A single impressed current ground bed at
mile 61 protects the entire line. There were no compressor stations in this section. The six
year old pipeline required 11 µA/m2 to achieve protection. 20 See Table 3 for the project CP
summary.
Table 3. Pertinent details of Case History 3.
Total Pipeline length 133 km
Micro amps/m2
11.0
Location of groundbed Mile 61Date of Installation 2002
In summary, many of the existing standards for cathodic protection current requirements and
projections for the requirements over the life of the pipeline are written by people with little
or no experience with FBE coated pipelines. For that reason, they include a very conservative
estimate of installation current requirements and high breakdown factors that do not fit actual
experience.
CONCLUSIONS
FBE systems have a long track record as effective pipeline coatings. FBE systems provide
pipeline owners also with an economically attractive, damage-resistant, and non-shieldingcoating system that can be used from one end of the pipeline to the other.
Another factor is application plant productivity. This is very plant specific, but frequently
throughput for DLFBE is 10% to 15% or even higher compared to 3-layer polyolefin
application. FBE coating materials are locally manufactured and do not require the long lead
times and storage facilities needed for imported polyolefin materials.
A factor that makes FBE systems effective in the prevention of underfilm corrosion is their
excellent adhesion to steel, high physical performance, low oxygen permeability and the
capability not to shield CP current.
It has been well documented that the weakest regions for corrosion protection on a pipeline
are the weld area and field joints. In such areas, it is considerably more likely that the rate of water and oxygen ingress will be high. In addition, the water, oxygen, and other aggressive
species are able to travel freely along the weld seam if poor surface cleaning was done, or an
overlapping weld cap is present. Cathodic shielding can allow corrosion in these areas. FBE
coated pipelines can utilize easily applied FBE coatings or two-part coating systems that
provide excellent performance and do not shield the steel from cathodic protection.
As a technology, FBE pipeline coatings continue to be important. Its success as a corrosion
mitigation system due to excellent chemical resistance, physical properties, ease of use, and
competitive pricing has lead to steadily increasing market share. FBE coatings consistently
meet the demands placed in a wide variety of industrial environmental applications. FBE
coatings have a successful track record for protecting pipelines around the globe – from the
highly aggressive environment of the Middle East region, to the extreme conditions in thearctic, to swamps, to mountains and to the ocean depths.
1A. Kehr, M. Mallozzi, Fast, worry free pipeline installation with dual-layer FBE Coatings, ACA Corrosion
Control 007, November 25-28, 2007, Sydney.2
D. G. Enos, J. A. Kehr, C. R. Guilbert, “A High-Performance, Damage-Tolerant, Fusion-Bonded Epoxy.3 H. Lee, K. Neville, Handbook of Epoxy Resins, (New York: McGraw-Hill Book Company, 1967).
4J. Alan Kehr, A Foundation of Pipeline Corrosion Protection. (Houston, NACE, 2003).
5J. Banach, “FBE: An End-User’s Perspective,” NACE TechEdge Program, Houston , Using Fusion Bonded
Powder Coating in the Pipeline Industry, June 1997.
C. G. Munger, Louis D. Vincent, Corrosion Prevention by Protective Coatings, 2nd
ed., (Houston, TX: NACE,
1999), p. 50.7
D. G. Temple, K. E. W. Coulson, “Pipeline Coatings, Is It Really a Cover-up Story? Part 2,” Paper 356,Corrosion 84, (Houston, TX: NACE, 1984), p.1.8
J. A. Kehr, D. G. Enos, “FBE, a Foundation for Pipeline Corrosion Coatings,” Corrosion/00, paper no. 00757,
(Houston, TX: NACE, 2000)9
C. G. Munger, Louis D. Vincent, Corrosion Prevention by Protective Coatings, 2nd
ed., (Houston, TX: NACE,1999), p. 53.10
Enviroline Laboratories, Letter of Certification, Minneapolis, MN, February 17, 1969.11
MIL-STD-810F(1), “Insulating Compound, Electrical, Embedding, Epoxy,” November 1, 2000, (Philadelphia,
PA: Document Automation and Production Service (DAPS), 2000).12
Bulletin No. 277, (Melbourne, Victoria: CSIRO, 1955), pp. 1 – 60.13 J. A. L. Watson, R. A. Barrett, “Report of Laboratory Tests to Determine the Termite Resistance of Protective
Plastic Coatings, Tapes, and Resins for Steel Pipe,” July 1975.14
Technical Paper No. 10, (Melbourne, Victoria: CSIRO, 1969), pp. 1 – 49.15
A. W. Peabody, Peabody’s Control of Pipeline Corrosion.16
ASME B31.8, “Gas Transmission and Distribution Piping Systems,” 1995, p 36.17
ASME B31.4, “Pipeline Transportation Systems for Liquid Hydrocarbons and Other Liquids,” 1998.18
B. Schow, telephone interview, April 11, 2008.19
Anonymous, data provider asked not to be identified, email, January 20, 2009.20
T. Fore, Kinder Morgan, telephone interview April 10, 2008.